1. Field of the Invention
The present invention relates to an addition-curable silicone composition, and relates particularly to an addition-curable silicone composition that yields a cured product with minimal surface tack and favorable strength properties, and a cured product of such a composition.
2. Description of the Prior Art
Addition-curable silicone rubber compositions form cured products that exhibit excellent properties of weather resistance and heat resistance and the like, as well as superior rubber-like properties such as hardness and elongation, and they are therefore used as coating materials and the like in a wide variety of applications (see Patent Document 1). However, because the resulting cured products also exhibit surface tack, dust adhesion becomes a problem when these compositions are used as coating agents or the like for electrical or electronic components.
Cured products formed from hard resins obtained from silicone varnishes exhibit minimal surface tack, meaning the problem of dust adhesion does not arise, but such cured products suffer from a different problem in that because they lack adequate shock resistance, they tend to be prone to cracking, and particularly to cracking caused by thermal shocks. Accordingly, in the field of electrical and electronic component packaging, there is considerable demand for a silicone composition capable of forming a cured product that does not suffer from dust adhesion to the cured product surface, and exhibits excellent levels of crack resistance and shock resistance. Furthermore, a composition that can be cured using conventional molding apparatus, and is a solid (specifically, a plastically deformable solid) or semisolid (i.e., a liquid with a very high viscosity) at room temperature is required.
It is known that adding a resin-form organopolysiloxane component to an addition-curable silicone rubber composition can improve the strength of the cured product. For example, Patent Document 2 discloses an improvement in the strength of the cured product by using a branched (in other words, resin-form) organopolysiloxane as the alkenyl group-containing organopolysiloxane that is subjected to an addition reaction with an organohydrogensiloxane. However, even in those cases where the strength of the cured product is increased by using a resin-form organopolysiloxane, surface tack and dust adhesion remain problems.
It is known that adding a resin-form organopolysiloxane component to an addition-curable silicone rubber composition can generally improve the strength of the cured product. However, even in those cases where the strength of the cured product is increased by using a resin-form organopolysiloxane, surface tack and dust adhesion remain problems. Furthermore, if a hard resin is used, then the shock resistance of the cured product is inadequate, and in particular, a significant problem arises in that the cured product is prone to cracking during thermal shock testing.
In an attempt to address these problems, an addition-curable silicone composition and a cured product thereof have been proposed in which the composition forms a cured product that is a hard resin and yet exhibits excellent flexibility and minimal surface tack, and can be easily molded using a conventional molding apparatus such as a transfer molding, compression molding or injection molding apparatus (Patent Document 3). Furthermore, a silicone lens formed using such a composition and an addition-curable silicone resin composition that is ideal for lens molding have also been proposed (Patent Document 4). Moreover, addition-curable silicone resin compositions that can be used favorably for encapsulating LED elements and the like have also been proposed (Patent Document 5 and Patent Document 6).
However, even with these addition-curable silicone resin compositions, the conventional technique wherein the vinyl group-containing silicone resin and the hydrosilyl group-containing silicone resin are synthesized separately and then combined is not only complex in terms of the steps required, but also suffers various other problems. For example, hydrosilyl group-containing silicone resins are almost always liquid, and the composition obtained upon combining the hydrosilyl group-containing silicone resin with the vinyl group-containing silicone resin is also liquid, which makes the composition difficult to handle as a molding resin.    [Patent Document 1] US2004/0214966A1    [Patent Document 2] JP2005-76003A    [Patent Document 3] US2007/0129508A1    [Patent Document 4] US2007/0249790A1    [Patent Document 5] US2007/0293623A1    [Patent Document 6] US2008/0021136A1